Magnesium alloy and preparation method thereof

Abstract

The invention provides a magnesium alloy and a preparation method thereof. Comprising a magnesium matrix, an aluminum element, a lanthanum element, a cerium element and a strontium element, the aluminum element, the lanthanum element, the cerium element and the strontium element exist in the magnesium matrix, and in the magnesium alloy, the mass percentage content of the aluminum element is 8.8%-12%, the mass percentage content of the lanthanum element is 0%-1.4%, the mass percentage content of the cerium element is 0%-1.4%, and the mass percentage content of the strontium element is 0%-0.4%. The magnesium alloy provided by the invention has the advantages of low cost, high corrosion resistance and no heat treatment.

Description

Technical Field

[0001] This invention relates to the field of alloys, and in particular to a magnesium alloy and its preparation method. Background Technology

[0002] With the rapid development of the global new energy vehicle industry, the demand for vehicle lightweighting is becoming increasingly urgent. Lightweighting is a key technological means to improve the driving range and reduce energy consumption of new energy vehicles. Against this backdrop, magnesium alloys, due to their excellent specific strength and damping properties among structural metals, have become the best candidate material for manufacturing key components of new energy vehicles, especially for electric drive system housing parts. Among the existing magnesium alloy grades, AZ91D is widely used in 3C products and body panels due to its good castability and low cost; however, this material has insufficient corrosion resistance. Electric drive housing parts for new energy vehicles, such as electronic control covers and resolver covers, are often directly exposed to the atmosphere, leading to corrosion problems. During vehicle operation, especially in rainy weather or on slippery roads, these housing parts are directly impacted by rainwater, de-icing agents, mud, and other corrosive media kicked up by tires, causing a sharp increase in corrosion. This not only affects the appearance of the product but may also cause serious malfunctions such as housing perforation and damage to internal precision electrical components, posing significant safety hazards. Therefore, promoting the application of magnesium alloys in electric drive housings and developing new die-cast magnesium alloys that combine low cost and high corrosion resistance have become key technological bottlenecks that the industry urgently needs to overcome.

[0003] To improve the corrosion resistance of magnesium alloys, existing technologies have been researched, but most suffer from limitations in cost, process, or performance. For example, patent document CN116716509A discloses an AZ91D modified magnesium alloy, which improves corrosion resistance by adding Ti to the alloy; however, Ti is expensive, and the alloy requires the ingot to be made into powder and then heated for semi-solid die casting, which is unsuitable for high-pressure die casting of electric drive housings. Patent document CN119710406A discloses a high corrosion-resistant magnesium alloy for automotive structural parts, which modifies and refines the microstructure by adding Hf to a Mg-Al-Zn alloy, achieving corrosion resistance slightly lower than ADC12 aluminum alloy; however, Hf is expensive, making mass production difficult. Patent document CN118880140B improves the corrosion resistance of magnesium alloys by adding Gd, Y heavy rare earth elements, Zr, and Ca, but Gd, Y heavy rare earth elements, and Zr are expensive. Patent document CN118272711A improves the corrosion resistance of magnesium alloys by adding Sm and Ca elements. However, Sm is expensive, and excessive Ca content exacerbates the alloy's hot cracking tendency, making it unsuitable for die casting. Furthermore, patent document CN116716509A, while improving corrosion resistance by adding excessive Ti, leads to poorer die casting performance and increased costs.

[0004] Therefore, there is an urgent need in this field to develop a heat-free magnesium alloy material and its supporting preparation method that is low-cost, highly corrosion-resistant, and suitable for high-pressure die casting processes, so as to truly meet the application requirements of electric drive housings for new energy vehicles. Summary of the Invention

[0005] This invention provides a magnesium alloy and its preparation method. This type of magnesium alloy has advantages such as low cost, high corrosion resistance and no need for heat treatment.

[0006] This invention provides a magnesium alloy comprising a magnesium matrix and aluminum, lanthanum, cerium, and strontium elements present in the magnesium matrix. In the magnesium alloy, the mass percentage of aluminum is 8.8%-12%, the mass percentage of lanthanum is 0%-1.4%, the mass percentage of cerium is 0%-1.4%, and the mass percentage of strontium is 0%-0.4%.

[0007] According to one embodiment of the present invention, in the magnesium alloy, the sum of the mass percentages of cerium and lanthanum is 0.3%-1.4%.

[0008] According to one embodiment of the present invention, the magnesium alloy further includes one or more of manganese, zinc, beryllium, nickel and iron elements present in the magnesium matrix.

[0009] According to one embodiment of the present invention, the manganese content is 0.01%-0.3% by mass; and / or, the zinc content is 0.01%-0.8% by mass; and / or, the beryllium content is 0.0005%-0.002% by mass; and / or, the nickel content is 0.001%-0.002% by mass; and / or, the iron content is less than 0.005% by mass.

[0010] According to one embodiment of the present invention, the magnesium alloy in the as-cast state has a yield strength greater than or equal to 160 MPa, a tensile strength greater than or equal to 255 MPa, and an elongation at break greater than or equal to 6%.

[0011] In another aspect, the present invention provides a method for preparing a magnesium alloy, comprising the following steps: die casting a third melt containing magnesium, aluminum, lanthanum, cerium and strontium to obtain the magnesium alloy.

[0012] According to one embodiment of the present invention, the process of die-casting a third melt containing magnesium, aluminum, lanthanum, cerium, and strontium includes: first melting a magnesium source to obtain a first melt; adding an intermediate alloy containing aluminum, zinc, manganese, and beryllium to the first melt, followed by a second melting, then adding a mixed rare earth element containing lanthanum and cerium, and metallic strontium, followed by a third melting to obtain a second melt; mixing the second melt with a refining agent and then refining it to obtain a third melt; and die-casting the third melt to obtain the magnesium alloy.

[0013] According to one embodiment of the present invention, the magnesium source includes one or more of magnesium shavings and magnesium ingots.

[0014] According to one embodiment of the present invention, the melting temperature of the first melting is 680℃-720℃, and the holding time is 0.5 h-3 h.

[0015] According to one embodiment of the present invention, the intermediate alloy includes one or more of MgAl, MgZn, MgMn, and AlBe.

[0016] According to one embodiment of the present invention, the melting temperature of the second melting is 700℃-750℃, and the holding time is 5min-15min.

[0017] According to one embodiment of the present invention, the grain size of the mixed rare earth is less than or equal to 20 μm.

[0018] According to one embodiment of the present invention, the refining temperature of the refining process is 650℃-710℃, and the holding time is 5 min-15 min.

[0019] According to one embodiment of the present invention, the refining agent includes MgCl2, KCl, and NaCl, wherein the mass ratio of MgCl2, KCl, and NaCl is (35-45):(30-40):(20-30).

[0020] According to one embodiment of the present invention, the die casting is performed using a die casting mold, and the conditions for the die casting are as follows: the vacuum degree of the die casting mold is 40 mbar-80 mbar, the injection speed is 2.0 m / s-2.5 m / s, the injection pressure is 40 MPa-100 MPa, the boosting pressure is 60 MPa-100 MPa, and the temperature of the die casting mold is 200℃-250℃.

[0021] In another aspect, the present invention provides a structural component comprising the aforementioned magnesium alloy or a magnesium alloy prepared by the aforementioned method.

[0022] In another aspect, the present invention provides an electric drive device including the aforementioned structural member.

[0023] The implementation of this invention has at least the following beneficial effects: The magnesium alloy provided by this invention, through the synergistic effect of four key elements—aluminum, lanthanum, cerium, and strontium—fundamentally optimizes the microstructure of the alloy, thereby achieving a balance between high corrosion resistance and good mechanical properties. Specifically, aluminum, as a basic alloying element, is the foundation for forming the strengthening phase. Adding lanthanum and cerium rare earth elements allows the highly reactive lanthanum and cerium to preferentially combine with aluminum during the alloy smelting process, forming thermodynamically stable and dense Al... 11 RE3 phase. Al 11 The formation of the RE3 phase helps to suppress the β-Mg, which has a large corrosion potential difference with the magnesium matrix (α-Mg). 17 Al 12 The precipitation of the phase improves the corrosion resistance of the alloy; in addition, Al 11 The RE3 phase forms and is structurally stable in the as-cast state, eliminating the need for further heat treatment to improve the alloy's structural properties. Strontium is an effective grain refiner, capable of refining the α-Mg matrix grains, thus reducing residual or incompletely suppressed Mg content. 17 Al 12 The phase is dispersed and discontinuously distributed, thus reducing its destructiveness; strontium can also combine with aluminum to form a dense Al4Sr phase, the corrosion potential difference between this phase and the magnesium matrix being relatively smaller than that of Mg. 17 Al 12 The lower concentration further reduces the overall self-corrosion tendency of the alloy. Simultaneously, by limiting the element content, this invention can both improve the corrosion resistance of the alloy and avoid the addition of excessive expensive elements, thereby reducing production costs. Detailed Implementation

[0024] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions in the embodiments of this invention will be clearly and completely described below in conjunction with the embodiments of this invention. The specific embodiments listed below are merely descriptions of the principles and features of this invention, and the examples given are only for explaining this invention and are not intended to limit the scope of this invention. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0025] This invention provides a magnesium alloy comprising a magnesium matrix and aluminum, lanthanum, cerium, and strontium elements present in the magnesium matrix. In the magnesium alloy, the mass percentage of aluminum is 8.8%-12%, the mass percentage of lanthanum is 0%-1.4%, the mass percentage of cerium is 0%-1.4%, and the mass percentage of strontium is 0%-0.4%.

[0026] According to the inventors' research, the aforementioned magnesium alloy, through the synergistic effect of four key elements—aluminum, lanthanum, cerium, and strontium—helps optimize the alloy's microstructure, thereby achieving a balance between high corrosion resistance and good mechanical properties. Specifically, aluminum, as a basic alloying element, forms the foundation for the strengthening phase. Adding lanthanum and cerium, rare earth elements, allows the highly reactive lanthanum and cerium to preferentially combine with aluminum during the alloy smelting process, forming thermodynamically stable and dense Al... 11 RE3 phase. Al 11 The formation of the RE3 phase helps to suppress the β-Mg, which has a large corrosion potential difference with the magnesium matrix (α-Mg). 17 Al 12 The precipitation of the phase improves the corrosion resistance of the alloy; in addition, Al 11 The RE3 phase forms and is structurally stable in the as-cast state, eliminating the need for further heat treatment to improve the alloy's structural properties. Strontium is an effective grain refiner, capable of refining the α-Mg matrix grains, thus reducing residual or incompletely suppressed Mg content. 17 Al 12 The phase is dispersed and discontinuously distributed, thus reducing its destructiveness; strontium can also combine with aluminum to form a dense Al4Sr phase, the corrosion potential difference between this phase and the magnesium matrix being relatively smaller than that of Mg. 17 Al 12 The lower concentration further reduces the overall self-corrosion tendency of the alloy. Simultaneously, by limiting the content of certain elements, this invention improves the alloy's corrosion resistance while helping to control production costs.

[0027] The mass percentage of aluminum can be 8.8%-12%, for example, 8.8%, 9%, 10%, 11%, 12% or any combination thereof; controlling the mass percentage of aluminum between 8.8% and 12% helps to provide sufficient aluminum to participate in the formation of the strengthening phase and to be dissolved in the magnesium alloy matrix, thereby providing good basic strength for the alloy.

[0028] The mass percentage content of lanthanum can be 0%-1.4%, for example, 0%, 0.4%, 0.8%, 1.2%, 1.4%, or any combination thereof; controlling the mass percentage content of lanthanum within the above range helps to generate stable Al11 RE3 phase inhibits β-Mg with high corrosion potential. 17 Al 12 The formation of the phase improves corrosion resistance; the mass percentage of lanthanum is no more than 1.4%, which helps control production costs and further improve die-casting performance.

[0029] The mass percentage of cerium can be 0%-1.4%, for example, 0%, 0.4%, 0.8%, 1.2%, 1.4%, or any combination thereof; controlling the mass percentage of cerium within the above range helps to generate stable Al. 11 RE3 phase inhibits β-Mg with high corrosion potential. 17 Al 12 The formation of the phase improves corrosion resistance; the mass percentage of cerium is no more than 1.4%, which helps control production costs and further improve die-casting performance.

[0030] The mass percentage of strontium can be 0%-0.4%, for example, 0%, 0.1%, 0.2%, 0.3%, 0.4% or any combination thereof; the strontium content should not exceed 0.4%, which helps to prevent the alloy from becoming less plastic, prone to hot cracking, or too expensive due to excessive addition.

[0031] In some embodiments, the sum of the mass percentages of cerium and lanthanum can be 0.3%-1.4%, for example, a range consisting of 0.3%, 0.6%, 0.9%, 1.2%, 1.4%, or any two of these. A mass percentage of La and Ce not less than 0.3% helps to provide sufficient Al. 11 RE3 phase, thereby suppressing β-Mg 17 Al 12 Phase formation; the mass percentage of La and Ce is not higher than 1.4%, which helps to improve the corrosion resistance of the alloy while controlling production costs and further improving die-casting performance.

[0032] In some embodiments, the magnesium alloy further includes one or more of manganese, zinc, and beryllium elements present in the magnesium matrix. The mass percentage content of the manganese element can be 0.01%-0.3%, for example, 0.01%, 0.05%, 0.1%, 0.2%, 0.3%, or any combination thereof; the mass percentage content of the zinc element can be 0.01%-0.8%, for example, 0.01%, 0.2%, 0.4%, 0.6%, 0.8%, or any combination thereof; the mass percentage content of the beryllium element can be 0.0005%-0.002%, for example, 0.0005%, 0.001%, 0.0015%. The mass percentage of nickel can be 0.001%-0.002%, for example, 0.001%, 0.0012%, 0.0014%, 0.0016%, 0.0018%, 0.002%, or any two of these ranges; the mass percentage of iron is less than 0.005%, for example, 0.001%, 0.002%, 0.003%, 0.004%, 0.005%, or any two of these ranges. Controlling the metal elements within the above ranges helps improve the corrosion resistance and mechanical properties of the alloy.

[0033] In some embodiments, the as-cast magnesium alloy has a yield strength greater than or equal to 160 MPa, a tensile strength greater than or equal to 255 MPa, and a fracture elongation greater than or equal to 6%. Controlling the as-cast yield strength, tensile strength, and fracture elongation of the magnesium alloy within the above ranges helps to improve the mechanical properties of the magnesium alloy.

[0034] In summary, the magnesium alloy provided by this invention, through the synergistic effect of four key elements—aluminum, lanthanum, cerium, and strontium—forms a stable Al alloy in the as-cast state. 11 The RE3 phase and the dispersed Al4Sr phase synergistically optimize the microstructure, thereby enabling the alloy to possess both excellent corrosion resistance and mechanical properties without heat treatment, while reducing production costs.

[0035] This invention also provides a method for preparing a magnesium alloy, comprising the following steps: die casting a third melt containing magnesium, aluminum, lanthanum, cerium and strontium to obtain the aforementioned magnesium alloy.

[0036] According to the inventors' research, the above-mentioned preparation method involves melting and die-casting key alloying elements through a specific process. The synergistic cooperation of each step is crucial to achieving a final product with high corrosion resistance, excellent mechanical properties, and heat-free characteristics. Specifically, aluminum, as a basic alloying element, forms the foundation for the strengthening phase; lanthanum and cerium rare earth elements combine with aluminum to form thermodynamically stable and dense Al.11 The RE3 phase suppresses the corrosion potential difference between β-Mg and the magnesium matrix (α-Mg). 17 Al 12 The precipitation of the phase helps to improve the corrosion resistance of the alloy; in addition, Al 11 The RE3 phase forms and is structurally stable in the as-cast state, eliminating the need for further heat treatment to improve the alloy's structural properties. Strontium is an effective grain refiner, capable of refining the α-Mg matrix grains, thus reducing residual or incompletely suppressed Mg content. 17 Al 12 The phase is dispersed and discontinuously distributed, thus reducing its adverse effects; strontium can also combine with aluminum to form a dense Al4Sr phase, the corrosion potential difference between this phase and the magnesium matrix being relatively smaller than that of Mg. 17 Al 12 The lower phase further suppresses the overall self-corrosion tendency of the alloy. The above preparation method enables the magnesium alloy to have good corrosion resistance and mechanical properties in the as-cast state, while avoiding subsequent heat treatment processes, providing an effective way to manufacture high-performance magnesium alloy structural parts at low cost.

[0037] In some embodiments, the process of die-casting the third melt containing magnesium, aluminum, lanthanum, cerium, and strontium includes: first melting a magnesium source to obtain a first melt; adding an intermediate alloy containing aluminum, zinc, manganese, and beryllium to the first melt, followed by a second melting; then adding a mixed rare earth element containing lanthanum and cerium, along with metallic strontium, and performing a third melting to obtain a second melt; refining the second melt with a refining agent to obtain a third melt; and finally die-casting the third melt to obtain the magnesium alloy. This step-by-step melting process helps reduce rare earth burn-off and promotes the full and uniform dissolution of each element, laying the foundation for subsequent die-casting of high-performance castings.

[0038] Specifically, the alloy preparation process described above is carried out in an inert gas atmosphere.

[0039] In some embodiments, the magnesium source includes one or more of magnesium shavings and magnesium ingots; such magnesium sources have the advantages of being readily available and low in cost.

[0040] In some embodiments, the melting temperature of the first melting point can be 680℃-720℃, for example, a range of 680℃, 690℃, 700℃, 710℃, 720℃, or any combination thereof; the holding time can be 0.5 h-3 h, for example, a range of 0.5 h, 1 h, 1.5 h, 2 h, 2.5 h, 3 h, or any combination thereof. Controlling the first melting temperature and holding time within the above ranges helps to ensure sufficient and uniform melting of the magnesium source, while avoiding energy waste and excessive oxidation of the melt caused by excessively high temperatures.

[0041] Specifically, the aforementioned magnesium alloy also includes manganese, zinc, and beryllium elements present in the aforementioned magnesium matrix; in the preparation method of the aforementioned magnesium alloy, the aforementioned intermediate alloy also contains one or more of manganese, zinc, and beryllium elements.

[0042] In some embodiments, the aforementioned intermediate alloy includes one or more of MgAl, MgZn, MgMn, and AlBe; the addition of such intermediate alloys helps to efficiently introduce alloying elements such as manganese, zinc, and beryllium.

[0043] In some embodiments, the melting temperature of the second melting point can be 700°C-750°C, for example, a range consisting of 700°C, 710°C, 720°C, 730°C, 740°C, or any two of these; the holding time can be 5 min-15 min, for example, a range consisting of 5 min, 7 min, 9 min, 11 min, 13 min, 15 min, or any two of these. Controlling the second melting temperature and holding time within the above ranges helps to dissolve the intermediate alloy and achieve compositional homogenization. A holding time of not less than 5 min helps to ensure dissolution and diffusion; a holding time of not more than 15 min helps to prevent excessively long production cycles and energy waste.

[0044] In some embodiments, during the third melting process described above, the mixed rare earth containing lanthanum and cerium needs to be extruded and deformed before being added, with a plastic deformation amount >0.2, so that the grain size of the mixed rare earth is less than or equal to 20 μm. The fine-grained La and Ce mixed rare earth has a higher grain boundary fraction and more high-energy atoms than before deformation, resulting in lower energy consumption for dissolution, faster and more complete dissolution, and better uniformity and consistency of the melt.

[0045] The aforementioned magnesium alloy also includes nickel and iron, which are unavoidable impurity elements introduced during the smelting process from raw materials and equipment. The mass percentage of nickel can be 0.001%-0.002%, for example, 0.001%, 0.0012%, 0.0014%, 0.0016%, 0.0018%, 0.002%, or any combination thereof; the mass percentage of iron is less than 0.005%, for example, 0.001%, 0.002%, 0.003%, 0.004%, 0.005%, or any combination thereof. Controlling the impurity elements within these ranges helps reduce the content of harmful impurity elements in the alloy, which is one of the important guarantees for obtaining high corrosion resistance.

[0046] In some embodiments, the refining agent includes MgCl2, KCl, and NaCl, and the mass ratio of MgCl2, KCl, and NaCl can be (35-45):(30-40):(20-30), for example, 35:30:20, 45:30:20, 35:40:20, 35:30:30, 45:40:20, 45:40:30, or any combination thereof. The refining agent helps remove inclusions and gases and improve melt quality through physical adsorption and chemical reaction; the slag phase containing elements such as K and Na produced by the refining agent is ultimately removed by skimming (manual or mechanical removal of surface scum).

[0047] In some embodiments, the refining temperature of the above-described refining process can be 650°C-710°C, for example, a range consisting of 650°C, 670°C, 690°C, 700°C, 710°C, or any two of these; the holding time can be 5 min-15 min, for example, a range consisting of 5 min, 7 min, 9 min, 11 min, 13 min, 15 min, or any two of these. Controlling the refining temperature and holding time within the above ranges helps to maintain good flowability and reactivity of the refining agent.

[0048] Specifically, when the aforementioned third melt is die-cast, the temperature of the third melt can be 670℃-690℃, for example, 670℃, 675℃, 680℃, 685℃, 690℃ or any combination thereof.

[0049] In some embodiments, the die casting process is performed using a die casting mold. The conditions for die casting are as follows: the vacuum level of the die casting mold can be 40 mbar-80 mbar, for example, a range consisting of 40 mbar, 50 mbar, 60 mbar, 70 mbar, 80 mbar, or any two thereof; a vacuum level of not less than 40 mbar is beneficial for cavity venting and reducing porosity in the casting, while a vacuum level of not more than 80 mbar helps control equipment load and production costs. The injection speed can be 2.0 m / s-2.5 m / s, for example, a range consisting of 2.0 m / s, 2.1 m / s, 2.2 m / s, 2.3 m / s, 2.4 m / s, 2.5 m / s, or any two thereof; an injection speed of not less than 2.0 m / s helps the melt fill the mold completely, while an injection speed of not more than 2.5 m / s helps reduce melt entrapment and decrease the tendency for internal shrinkage cavities. Injection pressure can be between 40 MPa and 100 MPa, for example, a range of 40 MPa, 50 MPa, 60 MPa, 70 MPa, 80 MPa, 90 MPa, 100 MPa, or any combination thereof. Injection pressure refers to the pressure applied by the injection punch to push the molten material into the mold cavity during the filling stage of the die casting process. An injection pressure of not less than 40 MPa helps ensure filling power, while an injection pressure of not more than 100 MPa helps reduce mold wear. Intensification pressure can be between 60 MPa and 100 MPa, for example, a range of 60 MPa, 70 MPa, 80 MPa, 90 MPa, 100 MPa, or any combination thereof. Intensification pressure refers to the higher pressure applied after the molten material has filled the mold cavity and at the moment of solidification. Controlling the intensification pressure within the above range can compensate for the shrinkage of the alloy during solidification. The temperature (i.e., the preset temperature) of the aforementioned die-casting mold can be between 200℃ and 250℃, such as 200℃, 210℃, 220℃, 230℃, 240℃, 250℃, or any combination thereof. A mold temperature not lower than 200℃ helps improve melt fluidity and prevent cold shut defects, while a mold temperature not higher than 250℃ helps control the solidification rate, avoid grain coarsening, and maintain production cycle time. Controlling the die-casting conditions within the above range has a synergistic effect, which helps improve melt fluidity, improve the quality of casting, and enhance its mechanical properties.

[0050] In practice, a magnesium source is first added to a melting furnace in an inert gas atmosphere and heated for the first melting to obtain a first melt. The first melt is then heated, and an intermediate alloy containing aluminum, zinc, manganese, and beryllium is added for the second melting. The reaction melting temperature is maintained, and then a mixed rare earth element containing lanthanum and cerium, as well as metallic strontium, are added for the third melting to obtain a second melt. The second melt is then cooled, and a refining agent is added and mixed for refining. After the reaction is complete, the melt is filtered to remove solid impurities, resulting in a third melt. The third melt is then injected into a mold cavity for die casting to obtain a magnesium alloy.

[0051] This invention also provides a structural component comprising the aforementioned magnesium alloy or a magnesium alloy prepared according to the aforementioned method. This structural component, containing the aforementioned magnesium alloy, has advantages such as low cost, high corrosion resistance, and no need for heat treatment, which will not be elaborated further.

[0052] This invention also provides an electric drive device including the aforementioned structural components. Such terminal devices, containing these structural components, offer advantages such as low cost, high corrosion resistance, and no need for heat treatment, which will not be elaborated further.

[0053] The present invention will be further described below through specific embodiments.

[0054] Example 1

[0055] The mass percentages of each element in the magnesium alloy formula are as follows: Al content is 9.3%, Zn content is 0.6%, La content is 0.1%, Ce content is 1.2%, Mn content is 0.18%, Sr content is 0.002%, Be content is 0.0005%, Ni content is 0.0014%, Fe content is 0.002%, and the balance is Mg, of which La+Ce content is 1.3%.

[0056] Methods for preparing magnesium alloys include:

[0057] S1. In the SF6 / CO2 mixed gas, a magnesium source is first added to a closed melting furnace and heated to 700℃ for the first melting. The temperature is held for 2 hours to allow the magnesium source to fully melt and homogenize, thus obtaining the first melt.

[0058] S2. The first melt is heated to 720℃, and then MgAl, MgZn, MgMn, and AlBe master alloys (used to introduce elements such as Al, Zn, Mn, and Be) are added for the second melting. The temperature is held for 5 min. The reaction melting temperature is maintained, and then mixed rare earth elements containing lanthanum and cerium, as well as metallic strontium, which have undergone extrusion deformation treatment (plastic deformation amount not less than 0.8, grain size less than or equal to 20 μm) are added to it for the third melting. The temperature is held for 5 min to obtain the second melt.

[0059] S3. Reduce the temperature of the second melt to 700℃, add refining agent and mix, then refine, keep warm for 10 min, filter the melt after the reaction to remove solid impurities, and obtain the third melt; wherein, the mass ratio of MgCl2, KCl and NaCl in the refining agent is 40%:35%:25%.

[0060] S4. The temperature of the third melt is reduced to 680°C and injected into the mold cavity for vacuum die casting (the conditions for die casting are: vacuum degree of the die casting mold is 60 mbar, injection speed is 2.3 m / s, injection pressure is 70 MPa, boosting pressure is 80 MPa, and the temperature of the die casting mold is 230°C) to obtain a magnesium alloy.

[0061] Example 2

[0062] The mass percentages of each element in the magnesium alloy formulation are as follows: Al content is 8.8%, Zn content is 0.58%, La content is 1.2%, Ce content is 0.15%, Mn content is 0.23%, Sr content is 0.1%, Be content is 0.0005%, Ni content is 0.0017%, Fe content is 0.003%, and the balance is Mg, of which the La+Ce content is 1.35%. The preparation method and conditions of Example 2 are the same as those of Example 1.

[0063] Example 3

[0064] The mass percentages of each element in the magnesium alloy formulation are as follows: Al content is 9.1%, Zn content is 0.7%, La content is 0.5%, Ce content is 0.1%, Mn content is 0.21%, Sr content is 0.34%, Be content is 0.0005%, Ni content is 0.0001%, Fe content is 0.001%, and the balance is Mg, of which the La+Ce content is 0.6%. The preparation method and conditions of Example 3 are the same as those of Example 1.

[0065] The technical difference between Example 4 and Example 1 is that the mass percentage of Al is different, while the mass percentage of other elements is the same as in Example 1, as detailed in Table 1; the preparation method and conditions of Example 4 are the same as those of Example 1.

[0066] The technical difference between Example 5 and Example 3 is that the mass percentage content of La is different, while the mass percentage content of other elements is the same as in Example 3, as detailed in Table 1; the preparation method and conditions of Example 5 are the same as those of Example 3.

[0067] The technical difference between Example 6 and Example 1 is that the mass percentage content of La is different, while the mass percentage content of other elements is the same as that of Example 1, as detailed in Table 1; the preparation method and conditions of Example 6 are the same as those of Example 1.

[0068] The technical features that differentiate Examples 7-8 from Example 1 are that the mass percentage of Ce is different, while the mass percentage of other elements is the same as in Example 1, as detailed in Table 1; the preparation methods and conditions of Examples 7-8 are the same as in Example 1.

[0069] The technical difference between Example 9 and Example 3 is that the mass percentage of Ce is different, while the mass percentage of other elements is the same as in Example 3, as detailed in Table 1; the preparation method and conditions of Example 9 are the same as those of Example 3.

[0070] Comparative Example 1

[0071] The mass percentages of each element in the magnesium alloy formula are as follows: Al content is 8.9%, Zn content is 0.4%, Mn content is 0.2%, Fe content is 0.001%, and the balance is Mg.

[0072] Methods for preparing magnesium alloys include:

[0073] S1. In the SF6 / CO2 mixed gas, a magnesium source is first added to a closed melting furnace and heated to 700℃ for the first melting. The temperature is held for 0.5 h to allow the magnesium source to fully melt and homogenize, thus obtaining the first melt.

[0074] S2. Heat the first melt to 720°C, then add MgAl, MgZn, MgMn and AlBe master alloys to perform a second melting, hold for 5 min to obtain the second melt.

[0075] S3. Reduce the temperature of the second melt to 700℃, add refining agent and mix, then refine, keep warm for 10 min, filter the melt after the reaction to remove solid impurities, and obtain the third melt; wherein, the mass ratio of MgCl2, KCl and NaCl in the refining agent is 40%:35%:25%.

[0076] S4. The temperature of the third melt is reduced to 680°C and injected into the mold cavity for vacuum die casting (the conditions for die casting are: vacuum degree of the die casting mold is 60 mbar, injection speed is 2.3 m / s, injection pressure is 70 MPa, boosting pressure is 80 MPa, and the temperature of the die casting mold is 230°C) to obtain a magnesium alloy.

[0077] The technical features that differentiate Comparative Example 2 from Example 1 are that the mass percentages of La and Ce are both 3%, while the mass percentages of other elements are the same as in Example 1, as detailed in Table 1; the preparation methods and conditions of Comparative Example 2 are the same as those of Example 1.

[0078] The technical features that differentiate Comparative Example 3 from Example 1 are as follows: the mass percentage of Sr is 1%, and the mass percentage of other elements is the same as that in Example 1, as detailed in Table 1; the preparation method and conditions of Comparative Example 3 are the same as those in Example 1.

[0079] Table 1

[0080]

[0081] The properties of the magnesium alloys in each embodiment and comparative example were tested using the following test methods, and the test results are shown in Table 2.

[0082] (1) Performance testing

[0083] Tensile properties of the alloy were tested at room temperature according to the national standard GB / T 228.1 "Metallic materials, tensile testing—Part 1: Test methods at room temperature," determining the yield strength, tensile strength, and elongation at break. An MTS-E45.105 universal tensile testing machine equipped with a 50 mm gauge length contact extensometer (Epsilon-SN e104941) was used. During the test, a beam displacement rate of 2 mm / min was adopted. The yield strength (Rp0.2) was determined using the 0.2% residual strain method based on the automatically recorded stress-strain curve. The highest point of the curve was taken as the tensile strength (Rm), and the elongation at break (A) was calculated based on the gauge length measurement after specimen fracture. All tests were conducted at room temperature of 23±5℃. The formula for calculating the elongation at break is as follows:

[0084]

[0085] Where: L0: the original gauge length of the sample; L u : The gauge length of the specimen after fracture.

[0086] (2) Corrosion rate test

[0087] The corrosion rate test of magnesium alloy in this invention refers to the national standard JB / T 7901-1999 "Metallic Materials - Laboratory Uniform Corrosion Full Immersion Test Method". The specific operation is as follows: The generated magnesium alloy cast sample (50 mm × 25 mm × 3 mm) is polished with 120 grit sandpaper, ultrasonically dried with anhydrous ethanol, and placed in a desiccator for later use. The initial mass (m0) of the sample is weighed; at room temperature, the sample is immersed in a 3.5% sodium chloride solution for 168 h; after immersion, the sample is removed. The cleaning of corrosion products refers to GB / T 16545-2015-2015 "Corrosion of Metals and Alloys - Removal of Corrosion Products from Corrosion Samples". First, the sample is gently mechanically cleaned in running water with a soft brush to remove loosely attached or loose corrosion products. The sample was then immersed in a prepared 1000 mL solution (200 g lead trioxide (CrO3) + 10 g silver nitrate (AgNO3) + 20 g barium nitrate [Ba(NO3)2] + distilled water) at room temperature for 1 min. It was then rinsed sequentially with deionized water and anhydrous ethanol, and dried with cold air. The treated sample was placed back in a desiccator and, after reaching room temperature, its final mass (m1) was accurately weighed. The formula for calculating the corrosion rate is as follows:

[0088]

[0089] In the formula:

[0090] S: Total exposed surface area of ​​the sample (cm²) 2 );

[0091] t: Total soaking time (h);

[0092] ρ: Density of the magnesium alloy being tested;

[0093] 8.76×10 7 365: Constants related to unit conversion.

[0094] Table 2

[0095]

[0096] As shown in Table 2, the magnesium alloys provided by this invention exhibit balanced and excellent comprehensive properties. Regarding mechanical properties, the yield strength, tensile strength, and elongation at break of the magnesium alloys in Examples 1-9 all meet the preset standard mechanical indicators, indicating that the magnesium alloys in Examples 1-9 possess high strength and high toughness in the as-cast state, meeting the requirements of structural components for load-bearing capacity and safety. In terms of corrosion resistance, the corrosion rates of Examples 1-9 are maintained at extremely low levels, significantly better than the magnesium alloys in Comparative Examples 1-3. This confirms that through the specific ratio and synergistic effect of elements such as aluminum, lanthanum, cerium, and strontium, a stable phase is successfully formed in the microstructure of the magnesium alloy, and harmful phases are suppressed, thereby achieving excellent corrosion resistance without heat treatment at its source.

[0097] Comparative Example 1, serving as a reference for a traditional alloy, exhibited the worst corrosion resistance, highlighting the importance of composition optimization. Comparative Examples 2 and 3 altered the compositional balance by excessively adding key elements (rare earth elements or strontium). Their test results showed that not only did the expected performance improvement fail to materialize, but it may also lead to fluctuations in mechanical properties and a sharp decline in corrosion resistance. This demonstrates the importance and necessity of the element content range defined in the claims of this invention; deviations from the optimized range will fail to achieve the expected synergistic effect and may even produce negative consequences.

[0098] In summary, the magnesium alloy provided by this invention has advantages such as low cost, high corrosion resistance, and no need for heat treatment.

[0099] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A magnesium alloy, characterized in that, The magnesium alloy comprises a magnesium matrix and aluminum, lanthanum, cerium, and strontium present in the magnesium matrix. The magnesium alloy contains 8.8%-12% aluminum by mass, 0%-1.4% lanthanum by mass, 0%-1.4% cerium by mass, and 0%-0.4% strontium by mass.

2. The magnesium alloy according to claim 1, characterized in that, In the magnesium alloy, the sum of the mass percentages of cerium and lanthanum is 0.3%-1.4%.

3. The magnesium alloy according to claim 1, characterized in that, The magnesium alloy also includes one or more of the following elements present in the magnesium matrix: manganese, zinc, beryllium, nickel, and iron.

4. The magnesium alloy according to claim 3, characterized in that, In the magnesium alloy, the mass percentage content of manganese is 0.01%-0.3%; And / or, the zinc element has a mass percentage content of 0.01%-0.8%; And / or, the beryllium content is 0.0005%-0.002% by mass; And / or, the mass percentage content of the nickel element is 0.001%-0.002%; And / or, the mass percentage of iron is less than 0.005%.

5. The magnesium alloy according to any one of claims 1-4, characterized in that, The magnesium alloy has a yield strength greater than or equal to 160 MPa, a tensile strength greater than or equal to 255 MPa, and an elongation at break greater than or equal to 6% in the as-cast state.

6. A method for preparing a magnesium alloy according to any one of claims 1-5, characterized in that, Includes the following steps: The magnesium alloy is obtained by die casting a third melt containing magnesium, aluminum, lanthanum, cerium and strontium.

7. The method for preparing the magnesium alloy according to claim 6, characterized in that, The process of die-casting the third melt containing magnesium, aluminum, lanthanum, cerium, and strontium includes: The magnesium source is first melted to obtain the first melt; An intermediate alloy containing aluminum, zinc, manganese and beryllium is added to the first melt. After a second melting, a mixed rare earth element containing lanthanum and cerium, as well as metallic strontium, is added to it, and a third melting is performed to obtain a second melt. The second melt is mixed with a refining agent and then refined to obtain a third melt. The third melt is die-cast to obtain the magnesium alloy.

8. The method for preparing magnesium alloy according to claim 7, characterized in that, The magnesium source includes one or more of magnesium shavings and magnesium ingots; And / or, the melting temperature of the first melting is 680℃-720℃, and the holding time is 0.5 h-3 h; And / or, the intermediate alloy includes one or more of MgAl, MgZn, MgMn, and AlBe; And / or, the melting temperature of the second melting is 700℃-750℃, and the holding time is 5min-15min; And / or, the grain size of the mixed rare earth is less than or equal to 20 μm; And / or, the refining temperature of the refining process is 650℃-710℃, and the holding time is 5 min-15 min; And / or, the refining agent includes MgCl2, KCl, and NaCl, wherein the mass ratio of MgCl2, KCl, and NaCl is (35-45):(30-40):(20-30).

9. The method for preparing magnesium alloy according to claim 7, characterized in that, The die casting process is carried out using a die casting mold, and the die casting conditions are as follows: the vacuum degree of the die casting mold is 40 mbar-80 mbar, the injection speed is 2.0 m / s-2.5 m / s, the injection pressure is 40 MPa-100 MPa, the boosting pressure is 60 MPa-100 MPa, and the temperature of the die casting mold is 200℃-250℃.

10. A structural component, characterized in that, This includes the magnesium alloy as described in any one of claims 1-5 or the magnesium alloy prepared according to the preparation method described in any one of claims 6-9.

11. An electric drive device, characterized in that, Includes the structural component as described in claim 10.

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